AdoHcyase

Adenosylhomocysteinase (S-adenosyl-L-homocysteine hydrolase, EC 3.3.1.1) (AdoHcyase) is an enzyme of the activated methyl cycle, responsible for the reversible hydration of S-adenosyl-L-homocysteine into adenosine and homocysteine. This enzyme is ubiquitous, highly conserved, and may play a key role in the regulation of the intracellular concentration of adenosylhomocysteine. AdoHcyase requires NAD+ as a cofactor and contains a central glycine-rich region which is thought to be involved in NAD-binding.

Mutational and nucleotide sequence analysis of S-adenosyl-L-homocysteinehydrolase from Rhodobacter capsulatus.

Proc Natl Acad Sci U S A. 1992; 89: 6328-32

Display abstract

The genetic locus ahcY, encoding the enzyme S-adenosyl-L-homocysteinehydrolase (EC 3.3.1.1) from the bacterium Rhodobacter capsulatus, has beenmapped by mutational analysis to within a cluster of genes involved inregulating the induction and maintenance of the bacterial photosyntheticapparatus. Sequence analysis demonstrates that ahcY encodes a 51-kDapolypeptide that displays 64% sequence identity to its human homolog.Insertion mutants in ahcY lack detectable S-adenosyl-L-homocysteinehydrolase activity and, as a consequence, S-adenosyl-L-homocysteineaccumulates in the cells, resulting in a 16-fold decrease in theintracellular ratio of S-adenosyl-L-methionine toS-adenosyl-L-homocysteine as compared to wild-type cells. The ahcYdisrupted strain fails to grow in minimal medium; however, growth isrestored in minimal medium supplemented with methionine or homocysteine orin a complex medium, thereby indicating that the hydrolysis ofS-adenosyl-L-homocysteine plays a key role in the metabolism ofsulfur-containing amino acids. The ahcY mutant, when grown in supplementedmedium, synthesizes significantly reduced levels of bacteriochlorophyll,indicating that modulation of the intracellular ratio ofS-adenosyl-L-methionine to S-adenosyl-L-homocysteine may be an importantfactor in regulating bacteriochlorophyll biosynthesis.